Epoxy resins are used for wide-ranging applications in view of their excellent curing physical properties and easiness of handling. In addition, the epoxy resins include a variety of kinds, and their curing physical properties are largely variable, and therefore, they are used for different purposes according to respective applications. For example, although the epoxy resins are used for semiconductor sealing, accompanying conspicuous development of electronic industry in recent years, requirements for heat resistance and insulation reliability required in electronic devices are becoming strict more and more.
For example, due to high integration of semiconductor devices, the upsizing of semiconductor elements and the downsizing and thinning of packages are advanced, and the mounting method also shifts to surface amounting. In this case, at the time of mounting, the whole of the semiconductor device is exposed to a high temperature close to a melting temperature of solder, and therefore, heat resistance is required. In recent years, the requirement for heat resistance becomes stricter due to an increase of the melting point accompanying lead-free processing of solder.
In addition, the requirement for an amount of impurities in the epoxy resin also becomes strict. In particular, in view of the matter that a sodium ion, a chloride ion, and so on cause problems, such as corrosion of metal, etc., resulting in impairing the reliability, it is general to reduce their contents as far as possible (see Patent Literatures 1 to 3).
On the other hand, tetramethylbiphenol type epoxy resins are excellent in crystallinity and have not only a high glass transition temperature (Tg) but also a low viscosity, and therefore, they are suitable for transfer molding and in particular, are widely used for a semiconductor sealing application (see Patent Literature 4).